Glycerol additive makes cruise ships greener

The bunker fuel used in cruise liners and freighters is some of the cheapest, crudest fuel available. It’s also among the dirtiest. Scientists from the Maine Maritime Academy and SeaChange Group LLC led by George N. Harakas, Ph.D announced at the 244th National Meeting & Exposition of the American Chemical Society that they have developed what they call "Bunker Green" fuel. This fuel uses an ingredient commonly used in food and medicine to reduce sulfur and other emissions in ocean vessels.

People talk about the “bottom of the barrel,” but bunker fuel literally is just that. Thick, viscous and cheap, it’s the dregs of the oil refining process. To the uninitiated, it resembles a sort of runny tar. But it will burn and large, slow-speed diesel engines can manage it. Because of its price, bunker fuel has been standard for large marine engines since the 1950s and is commonly used in freighters, cruise ships, tankers and other large ships.

The problem is that bunker fuel is very dirty. There’s too much sulfur in it and it’s often contaminated with all manner of elements. Air pollution is of particular concern when such ships steam close to shore and enter urban harbors and in recent years, a lot of pressure has come to bear on passing laws to reduce emissions.

Bunker Green is a simple fuel additive for bunker fuel. It’s glycerol, which is a colorless, odorless, the byproduct of soap manufacturing and biodiesel refining. It’s used in medicines, sweeteners, cosmetics and as a filler in low-fat foods. Because glycerol mixes with oil about as well as water does, a surfactant is used to reduce the surface tension of the liquid. Detergents are one example of a surfactant whose addition allows the glycerol to mix with the bunker fuel.

This simple addition has impressive results. According to the team’s report, the additive helps remove the sulfur and reduces soot emissions by 15 percent and nitrogen oxide by 26 percent.